This invention relates to the protection of computers and other electronic devices of the type that can be attached to a network of such devices.
U.S. Pat. No.3,983,338 teaches a switch and a resistor or capacitor mounted in a telephone connector jack. These components supplement the ringing circuits that were also used to detect unauthorized telephone sets on a subscribers line. The switch allows the phone company to determine the operability of the subscriber line even when the subscriber has unplugged all phones. This patent also discusses monitoring other lines and the equipment attached thereto for the purpose of detecting the removal of equipment such as amplifiers by theft or inadvertence. Checking is accomplished by sending a signal over the line to the subscribers station and measuring the amount of deviation produced in the signal by the components at the station. These teachings require the jacks at all subscriber stations to be changed which is not a practical solution.
U.S. Pat. No. 3,982,180 teaches apparatus for testing for continuity, shorts and correct connection of multiconconductor cables. A plurality of zener diodes are connected to the cable wires at one end and a DC voltage and resistance is selectively connected to the other ends of the cable wires while monitoring the currents generated in the wires. These teachings are impractical for the purposes of the instant invention because one must enter to each subscriber station to connect the diodes.
U.S. Pat. No. 4,551,671 teaches apparatus for detecting faults in the wiring connections to data terminal equipment. Pluggable connectors and wall connectors of the self shorting type are used and test currents are measured.
U.S. Pat. No. 4,491,838 teaches a star loop network. The network operates as a loop circuit during normal operation but becomes a star configuration for trouble shooting.
U.S. Pat. No. 4,924,457 teaches apparatus for detecting and stopping tariff charges on intra-office connections.
U.S. Pat. No. 4,519,070 teaches message re-routing in response to the power-on or fault status of connections to other stations in the network.